Investigation of the synthesis and degradation of liver pyruvate kinase (LPK) as a mechanism to control the enzyme activity in liver. Approaches include in vivo measurements of the turnover of liver pyruvate kinase after pulse labeling with a radiolabeled amino acid. The RNA from livers of animals in various dietary states will be isolated and translated in vitro to investigate whether changes in LPK synthesis involve translation or transcription control, or both. The rapid hormone elicited phosphorylation of liver pyruvate kinase is also being investigated. The stoichiometry of phosphorylation in response to a variety of hormones, the specific peptides of pyruvate kinase being phosphorylated, and change in the proteolytic degradation of pyruvate kinase after phosphorylation are some of the specific questions currently under investigation. Changes in catalytic activity are being correlated with the chemical and physical modifications of the enzyme in response to the phosphorylation and proteolytic activities.